In Vitro Evaluation of Acute Toxicity of Five Citrus spp. Essential Oils towards the Parasitic Mite Varroa destructor

Abstract

Varroa destructor is the most important ectoparasitic mite of honey bees that has a negative impact on bee health and honey production. The control programs are mainly based on the use of synthetic acaricides that are often administered indiscriminately. All this has led to drug resistance that now represent a great concern for honey bee farming. The research for alternative products/methods for mites’ control is now mandatory. The aim of this study was to test whether Citrus spp. essential oils could diminish the growth of the V. destructor mite. In Calabria (southern Italy), plants of the Citrus genus are very common and grow both spontaneously and cultured. The essential oils used in this study were extracted from bergamot (Citrus bergamia), grapefruit (Citrus paradisi), lemon (Citrus limon), orange (Citrus sinensis), and mandarin (Citrus reticulata) by hydrodistillation. Every EO was in vitro tested against V. destructor. Each experimental replicate was performed using 35 viable adult female mites (5 for each EO) collected the same day from the same apiary and included negative controls (5 individuals exposed to acetone only) and positive controls (5 individuals exposed to Amitraz diluted in acetone). The essential oils (Eos) were diluted (0.5 mg/mL, 1 mg/mL, and 2 mg/mL) in HPLC grade acetone to obtain the working solution to be tested (50 µL/tube). Mite mortality was manually assessed after 1 h exposure under controlled conditions. The essential oils that showed the best effectiveness at 0.5 mg/mL were bergamot, which neutralized (dead + inactivated) 80% (p ≤ 0.001) of the parasites; grapefruit, which neutralized 70% (p ≤ 0.001); and lemon, which neutralized 69% of them. Interestingly, the positive control (Amitraz) at the same concentration neutralized 60% of the parasites. These results demonstrate that Calabrian bergamot, grapefruit, and lemon Eos consistently reduced V. destructor viability and open the possibility for their utilization to control this parasite in honey bee farming.

Green Veterinary Pharmacology for Honey Bee Welfare and Health: Origanum heracleoticum L. (Lamiaceae) Essential Oil for the Control of the Apis mellifera Varroatosis

“…The methods of Gashout and Guzmán-Novoa (2009) [ 48 ], adapted from Bava et al (2021) [ 26 ], to assess the acute toxicity of essential oil for mites have been used.…”

“…The identification of alternative methods for the control of V. destructor becomes urgent, also in the light of the increasingly and widespread phenomena of drug resistance reported [ 21 , 22 , 23 , 24 , 25 ]. Control methods based on the use of essential oils offer considerable promise due to their low toxicity to humans and the environment [ 26 ].…”

“…Thanks to their particular and diversified chemical composition, the parasitic populations treated with essential oils are often unable to develop drug resistance phenomena [ 26 , 28 , 29 ].…”

Entomopathogenic Fungi for Pests and Predators Control in Beekeeping

“…Therefore, the use of entomopathogenic fungi could represent a promising tool to achieve an eco-friendly approach and could be a prospective approach for the near future in beekeeping [160].…”

“…In conclusion, the entomopathogenic fungi are important as they are environmentally friendly, they do not cause resistance phenomena in parasites, they are safe for the host and interrupt the life cycle of the parasite [160]. This also reduces the transmission of various pathogens, such as bacteria and viruses, with indisputable benefits for bee welfare and health.…”